1. Field of the Invention
A magnetic device according to the present invention can be utilized over a wide range such as a magnetic memory, a magnetic sensor and a spin operational device. Particularly, the present invention is useful as a part of a solid-state magnetic memory device.
2. Related Background Art
Conventionally, for a solid-state memory device, DRAM, SRAM, flash memory, EEPROM and FeRAM have been used. In recent years, however, from the viewpoints of non-volatility, higher speed and higher density, a magnetic solid memory, particularly a memory using a TMR or GMR effect has attracted much interest and its study has advanced. In the following description, a solid-state magnetic memory closely related to the present invention will be described.
First, a giant magneto-resistance (GMR) will be simply described. As regards the GMR, a magnetio-resistive change larger than an AMR (Anisotropic Magnetic Resistance) was discovered with ferromagnetic (Fe)/non-magnetic (Cr) (Chromium) artificial lattices by Fert et al. and Grunberg et al. in 1986 to 1988, and this has been called xe2x80x9cGiant Magneto-Resistance, GMRxe2x80x9d. This GMR has a special feature that it has a negative rate of change of resistance with respect to an applied magnetic field and has a great (a few tens percent) change in resistivity. The cause of GMR is qualitatively explained as follows. First, when there is no magnetic field, magnetic layers of the artificial lattice are arranged in an antiferromagnetic way (interlayer antiferromagnetism). When a magnetic field is applied in this case, magnetization of each layer is arranged in parallel. At this time, conduction arranged electrons are strongly scattered in a magnetizing non-parallel state, and the electric resistance decreases by the magnetic field by means of a mechanism having a dependence on such a spin as weakly scattered in a magnetizing parallel state. Theoretically, non-parallelism of interlayer magnetization has been studied by the use of a RKKY type long-distance exchange interaction or a quantum well model, and interlayer spin-dependent scattering has been discussed by a theory based on a binary fluid model of conduction electrons.
In order to utilize this GMR effect as a device such as a memory, the orientation of magnetization of a partial ferromagnetic layer is fixed while the orientation of magnetization of the other ferromagnetic layer is changed to use it as a memory. A device having such a structure is called xe2x80x9cspin valve typexe2x80x9d. Also, a layer (layer having a high coercive force), the orientation of magnetization of which remains unchanged, is called xe2x80x9chard layer (pin layer)xe2x80x9d while a layer (layer having a low coercive force), the orientation of magnetization of which is changed, is called xe2x80x9cfree layerxe2x80x9d. Contrary to this, there has also been adopted a method of reading a state of magnetization (memory state) from the change in resistance by recording on the hard layer and reversing the free layer.
Concerning this GMR, there have been known CIP (Current in Plane) type, CPP (Current Perpendicular to Plane) type, CPA (Current at an Angle) type, which is a type of their mixture, granular alloy type or the like. Generally, the CIP structure has most been studied in terms of its ease of fabrication. However, the CIP type, in which electric current flows in parallel with a lamination interface, has a change in resistivity being 40 to about 50% because of contribution of conduction electrons which do not interface spin scattering, or the like. In contrast, the CPP type, in which electric current flows in a direction perpendicular to the lamination interface, may have a change in resistivity exceeding 100% because of all electrons being exposed spin scattering having a dependence on the spin state on the lamination interface, an effect of increased Fermi velocity based on an energy gap resulting from the laminated structure, or the like, and the CPP type has better basic characteristics.
However, since the CPP type flows electric current in a direction perpendicular to the film surface, its resistance itself tends to become a very small value. For this reason, a pore enveloping the laminated structure must be made into a shape having a very small cross-sectional area.
In the CPP type GMR device into a pore, as an example of a structure which is not a simple laminated structure having a ferromagnetic layer/non-magnetic layer, there is one specified in Applied Physics Letters Vol. 70, 396 (1997). In this paper, there is specified an example in which lamination is performed with three-layer structure of NiFe alloy/Cu/NiFe alloy interposed between thick Cu layers, and this operation provides an effect in which the saturation magnetic field decreases. In this example of configuration, however, any sufficient memory effect has not yet appeared.
Also, as an example showing the memory effect, there is one specified in Applied Physics Letters Vol. 76, 354 (2000). In this paper, it is specified that the configuration is arranged such that a ferromagnetic layer (free ferromagnetic layer 14) having a thin layer is interposed between a ferromagnetic layer (hard layer 61) having such a thick layer as shown in FIG. 6A and a non-magnetic layer 62 for lamination, whereby a memory effect having a change in resistance being about 10% is exhibited. However, the reversal of this memory state is not clear.
 less than Tunnel Type Magnetic Memory greater than 
As a memory cell using a tunnel junction, such a spin valve type as disclosed in U.S. Pat. No. 5,764,567 specification has generally been used. Such a cell has a laminated structure of a pin layer, an insulating layer, a ferromagnetic layer or the like. The orientation of magnetization in the ferromagnetic layer is directed toward one of the longitudinal axes of an ordinary cell. Particularly when the orientations of two ferromagnetic layers with an insulating layer interposed therebetween are same, the tunneling current is increased, and the cell resistance value decreases. On the contrary, when the orientations of two ferromagnetic layers with an insulating layer interposed therebetween are opposite, the tunneling current decreases, and the cell resistance value is increased. As shown in FIG. 6B, as regards the orientation of magnetization of this ferromagnetic material layer, of two magnetic material layers normally, one magnetic material layer (pin layer 61) is left fixed with an antiferromagnetic layer 63, and the orientation of magnetization of the other magnetic material layer (free ferromagnetic layer 14) is changed. In the figure, the non-magnetic layer 62 is the insulating layer. The orientation of magnetization of this free ferromagnetic layer 14 is controlled and held by a magnetic field generated by electric current flowing through up and down wiring of the element. Generally, by means of a vector sum of the magnetic field to be generated by the up and down wiring orthogonally intersecting, only a selected cell portion is written. Reading-out is performed through a reading-out line or the like wired on the cell. The cell is selected by MOSFET or the like.
The rate of change of resistance of the TMR type can be made infinitely high in calculation, but values which can actually be fabricated are about 40 to about 60%. Also, it is how to fabricate the insulating layer and dependency of the rate of change of resistance on bias that most matter in fabrication and characteristics. More specifically, it is necessary to uniformly fabricate insulating layers having thickness of about 1 nm, but it is difficult to fabricate. Also, when the voltage is made higher, there arises a problem of dependency on bias that the rate of change of resistance will greatly decrease. These problems did not exist with the GMR device.
Since the present invention uses the GMR structure of CPP type, a pore having a large aspect ratio becomes necessary. As a method of obtaining this structure, a membrane filter using track etching and anodized alumina are known. Hereinafter, the detailed description will be made of the most preferable anodized alumina.
 less than The Anodized Alumina greater than 
When an Al plate is anodized in acid electrolyte such as sulphuric acid, oxalic acid, and phosphoric acid, an anodized alumina layer, which is a porous anodization film, is formed (See, for example, R. C. Furneaux, W. R. Rigby and A. P. Davidson NATURE Vol. 337P147 (1989) or the like.). The special feature of this porous film is to have a peculiar geometric structure in which exceedingly minute cylindrical column-shaped pores (nanoholes) having a diameter of several nm to several hundred nm are arranged at intervals of several tens nm to several hundred nm in parallel. Each of these cylindrical column-shaped pores has a high aspect ratio, and is also excellent in uniformity of diameter of the cross section.
Also, the structure of the porous film can be controlled to a certain extent by changing the condition for anodizing. For example, it has been known that the pore interval can be controlled by anodizing voltage, the pore depth can be controlled by anodizing time, and the pore diameter can be controlled to a certain extent by a pore wide treatment. The pore wide treatment here is etching of alumina, and normally, a wet etching treatment in phosphoric acid is used.
Also, in order to improve perpendicularity, linearity and independence of the pore of porous film, there has been proposed a method of anodizing in two stages, that is, a method of producing porous film having pores showing better perpendicularity, linearity and independence by removing porous film formed by anodizing once, and thereafter anodizing again (Japanese Journal of Applied Physics, Vol. 35, Part 2, No. 1B, pp. L126-L129, Jan. 15, 1996. This method takes advantage of the fact that a recess on the surface of an Al plate, which is produced when the anodized film formed by the first anodizing is removed, becomes a formation starting point of the pore by the second anodizing.
Further, in order to improve controllability of the shape, interval and pattern of pores of porous film, there has also been proposed a method of forming a formation starting point for the pores using a stamper, that is, a method of fabricating porous film having pores showing better controllability of shape, interval and pattern by forming a recess obtained by pressing a substrate having a plurality of projections on the surface thereof against the surface of an Al plate, as a formation starting point for pores, and thereafter, anodizing (U.S. Pat. No. 6,139,713 specification or Masuda""s Solid State Physics 31,493 (1996) or the like). Also, there has also been reported a technique for forming pores concentrically instead of honeycomb (Japanese Patent Application Laid-Open No. 11-224422 or the like).
Also, in Japanese Patent Application Laid-Open No. 10-283618 specification, there has been disclosed a technique for embedding laminated magnetic film having GMR characteristics into such an anodized alumina nanohole as described above. This specification discloses a technique for forming a hard ferromagnetic layer and a free ferromagnetic layer by taking advantage of a difference in composition, but its rate of change of resistance is about 10% and the memory effect is also insufficient.
The general GMR magnetic device previously described has a rate of change of resistance being about 40% because it is of the CIP type, and is insufficient. Also, in the GMR device of the CPP type, the stability and uniformity of the hard layer were insufficient.
An object of the present invention is to solve these problems of the prior art, and is to provide a magnetic device easy to fabricate, with higher density, having a laminated structure excellent in stability of a hard layer within a cell having a large aspect ratio even in the CPP type GMR device, which generates an initial state of magnetization of the hard layer and the free layer more easily and with stability, and a solid-state magnetic memory with the magnetic device.
The above-described object according to the present invention can be attained by a magnetic device, having a pore layer, on the substrate of which pores have been formed, in which in a part or all of the interior of the pores, a ferromagnetic layer and a non-magnetic layer are laminated, and which is used by applying electric current in the axial direction of the pores, wherein in the laminated structure within the pores, the plurality of ferromagnetic layers comprise a hard layer, which is a laminated structure portion having antiferromagnetic coupling through the non-magnetic layer, and a free ferromagnetic layer laminated through a non-magnetic layer; and a solid-state magnetic memory having the magnetic device.
According to an aspect of the present invention, there is provided a magnetic device which has a layer having pores on a substrate and is to be used by applying electric current in the direction of depth of the pores, comprising: a laminated structure in which ferromagnetic layers and non-magnetic layers are laminated within a part or all of the pores, wherein a hard layer and a free ferromagnetic layer are laminated through the non-magnetic layer, and the hard layer further has a laminated structure in which a plurality of ferromagnetic layers form antiferromagnetic coupling through the non-magnetic layers.
According to another aspect of the present invention, there is provided a solid-state magnetic memory having the magnetic device.